[JohnH]

I am taking longer exposures with my DSLR now that I have autoguiding working (mostly). A couple of questions arise, attached is a 16*300s stack of iso1600 images of NGC253, darks, flats and bias applied in IP2.8 and then I selected digital development, auto.

It appears I do not have anything like enough signal yet - this is shown by the amp glow? I thought darks would do a better job of getting rid of that but maybe not when you push this hard? So what is better - more subs or longer subs? What is a reasonable amount of exposure time for this object (200mm scope)?

The other observation I have is there is image shift from frame to frame (the black bar at bottom of frame shows area covered by only some of the frames) but - the system was autoguided and the guide s'ware reported no such shift - I do not think this is field rotation - the shift is in RA and consistant across the frame. Is this the dreaded differential flexure?